Such valve assemblies are known from the literature and comprise a valve housing having a valve seat and a valve body adapted to fit together in a closing relationship when in a closed position, and being positioned in the flow path of a fluid, which is being sprayed while the distance between said valve seat and said valve body is gradually increased.
One of the known valve assemblies is illustrated in e.g. EP 0 228 363, wherein the valve is part of a complete spray nozzle assembly, and it comprises a fixed solid valve body and a moveable tubular valve seat having a radial ring-shaped protrusion on the outer surface thereof, which protrusion is retained in a closing position against the valve body due to the axial force of a compression spring acting on the protrusion.
Releasing the closing position by gradually increasing the distance of the valve seat from the valve body allows an increasing flow of spray fluid to pass through the valve.
Said release is provided by forcing a hydraulic fluid into a circumferential chamber on one side of the radial protrusion opposite the compression spring.
The opening force required should be stronger than the combined force from the compression spring and the pressurized spray fluid acting on the cross sectional area of the tubular valve seat.
This means that the hydraulic fluid should provide a rather demanding force in order to initiate opening the valve, whereafter the hydraulic force needs to be decreased very fast or else the valve will immediately open fully. This means that an on-off valve has been provided rather than a linear regulation valve.